One type of tension tool is a banding tool for which the disclosed embodiment of the present invention is particularly adapted. An exemplary banding tool is shown in co-pending application Ser. No. 07/681,557 filed Apr. 5, 1991 and assigned to the assignee of the present invention, the disclosure of which is hereby incorporated by reference. As described therein, banding tools are utilized for tightening a band about an object to within preselected tension limits. One specific application is to tighten and secure a metal band about a woven metal braid portion of an electrical cable about a tubular termination sleeve portion of an electrical connector. In general, a banding tool includes a housing, a reciprocal shuttle mounted in the housing for gripping a band, and a pivotable lever coupled to the shuttle and extending from the housing. Actuation of the lever causes motion of the shuttle in a direction to effect tightening of the band. A return spring is coupled to the lever to return the lever to L ion The shuttle has a first part a non-actuated posit which supports the grip and a second part which connects to the lever arm. A spring holds the second part in a preselected position with respect to the first part. The second part is movable with respect to the first part when tension exerted on the band exceeds the instantaneous force of the spring. A trip mechanism is connected to the lever and arranged to transition to a tripped position when the lever is moved to a preselected end position. The shuttle is reciprocally moved a preselected distance by motion of the lever. This distance allows the linkage to retract from an overcenter position in response to force from the return spring. Relative displacement between the first and second parts of the shuttle limits reciprocal motion of the shuttle to a second distance less than the preselected distance when tension on the band is within the preselected tension limits whereby the trip mechanism is forcibly retained in the tripped position to prevent release of the lever to the non-actuated position.
The first part of the shuttle includes forward and aft members. The forward member has a slot extending therethrough for passage of a band. A pawl pivotally mounted to the forward member is adjacent the slot. One end of the pawl intersects the slot when the pawl is pivoted in a first direction. A linkage element connects a second end of the pawl and the aft member with a spring positioned between the forward member and the aft member for urging the members in opposite directions until retrained by the link. The pawl is pivoted in the first direction when the forward member is spaced from the aft member and the pawl is urged in a second direction for releasing a band in the slot when the aft member is urged toward the forward member.
The above mentioned spring, which sets the band tension limit at which the lever (or trigger) is held in a retracted position by virtue of the force on the trip mechanism, is disclosed as a stack of Belleville washers. The band tension limit is set by adjusting a screw to compress the washers. Although the washers are relatively stable in maintaining their set tension limit, ordinary wear and vibration of the tool may result in variation in the set limit. It is therefore desirable to provide a method and apparatus for periodically calibrating such banding tools.